Fragile-X carrier screening and the prevalence of premutation and full-mutation carriers in Israel

Prevalence and implications of fragile X premutation screening in Thailand

The fragile X premutation is a public health concern worldwide. Implementing a comprehensive screening program for FMR1 premutation alleles could empower individuals and families with information, supporting informed health decisions and potentially reducing the incidence of fragile X syndrome (FXS). This study aimed to determine the prevalence of FMR1 premutations in the Thai population. We screened 369 female blood donors and 449 males with tremor and/or ataxia who tested negative for spinocerebellar ataxia (SCA) types 1, 2, and 3 for FMR1 CGG repeat expansions. Among the female blood donors, 0.27% (1/369) had a premutation allele, and 1.08% (4/369) had intermediate alleles. One female with a premutation carrier had 89 CGG repeats with one AGG interruption. In the male cohort, no premutations or full mutations were found; however, intermediate alleles were identified in 0.67% (3/449) of the males. This study provides the evidence of fragile X premutation screening in the Thai population. These findings contribute to the understanding of FMR1 premutation prevalence in Thailand and should encourage wider discussions on the feasibility for a national fragile X carrier screening program in Thailand to reduce the burden of fragile X-associated disorders.

Strategic Implementation of Fragile X Carrier Screening in China: A Focused Pilot Study

Fragile X syndrome is the leading genetic cause of intellectual disability and autism spectrum disorders. Female premutation carriers exhibit no obvious symptoms during reproductive age, but the premutation allele can expand to full mutation when transmitted to the fetus. Given the relatively low prevalence but large population, the distinct health care system, the middle-income economic status, and low awareness among public and medical professionals, the optimal genetic screening strategy remains unknown. We conducted a pilot study of Fragile X carrier screening in China, involving 22,245 pregnant women and women with childbearing intentions, divided into control and pilot groups. The prevalence of Fragile X carriers in the control group was 1 of 850, similar to East Asian populations. Strikingly, the prevalence of Fragile X carriers in the pilot group was 1 of 356, which can be attributed to extensive medical training, participant education, and rigorous genetic counseling and testing protocols. Cost-effectiveness analyses of four strategies-no screening, population-based screening, targeted screening, and our pilot screening-indicated that our pilot screening was the most cost-effective option. A follow-up survey revealed that 55% of respondents reported undergoing screening because of their family history. We have successfully established a standardized system, addressing the challenges of low prevalence, limited awareness, and genetic testing complexities. Our study provides practical recommendations for implementing Fragile X carrier screening in China.

Attitudes of medical professionals toward fragile X carrier screening and genetic counseling in China

Fragile X syndrome is the most common inherited cause of intellectual disability. Considering China's low prevalence, distinct healthcare system, middle-income economic status, and unique culture, China cannot simply replicate the screening systems in European and American countries. In this study, we investigated the attitudes of 450 Chinese medical professionals who received fragile X training on fragile X carrier screening and genetic counseling. Before the training, 57.6% of the respondents were unfamiliar with FXS. After the training, 7.3% of participants are unable to fully master the knowledge. Furthermore, 71.8% believe that the absence of phenotypes during the reproductive age and the availability of simple and feasible testing methods are prerequisites for screening. The presence of the phenotype would still require screening. Regarding the target population, over 90% of the participants support fragile X carrier screening in high-risk pregnant women. As for influencing factors, they consider cost as the most influential factor in pregnant women's decision to undergo screening. The acceptable price range for screening is determined to be ￥200-1000 ($30-150). In terms of the issues and challenges of screening, most medical professionals support the need for genetic counseling for intermediate alleles and 55-60 repeat premutation results. Additionally, some respondents believe that informing patients' family members of positive screening results is necessary. It is also recognized that positive results may lead to anxiety for patients. The findings of this study will provide valuable information for the establishment of fragile X carrier screening system, particularly for low-prevalence or middle-income countries.

Atypical vocal quality in women with the FMR1 premutation: an indicator of impaired sensorimotor control

Women with the FMR1 premutation are susceptible to motor involvement related to atypical cerebellar function, including risk for developing fragile X tremor ataxia syndrome. Vocal quality analyses are sensitive to subtle differences in motor skills but have not yet been applied to the FMR1 premutation. This study examined whether women with the FMR1 premutation demonstrate differences in vocal quality, and whether such differences relate to FMR1 genetic, executive, motor, or health features of the FMR1 premutation. Participants included 35 women with the FMR1 premutation and 45 age-matched women without the FMR1 premutation who served as a comparison group. Three sustained /a/ vowels were analyzed for pitch (mean F0), variability of pitch (standard deviation of F0), and overall vocal quality (jitter, shimmer, and harmonics-to-noise ratio). Executive, motor, and health indices were obtained from direct and self-report measures and genetic samples were analyzed for FMR1 CGG repeat length and activation ratio. Women with the FMR1 premutation had a lower pitch, larger pitch variability, and poorer vocal quality than the comparison group. Working memory was related to harmonics-to-noise ratio and shimmer in women with the FMR1 premutation. Vocal quality abnormalities differentiated women with the FMR1 premutation from the comparison group and were evident even in the absence of other clinically evident motor deficits. This study supports vocal quality analyses as a tool that may prove useful in the detection of early signs of motor involvement in this population.

Executive Function and Working Memory Deficits in Females with Fragile X Premutation

The Fragile X premutation is a genetic instability of the FMR1 gene caused by 55–199 recurrences of the CGG sequence, whereas there are only 7–54 repeats of the CGG sequence in the normal condition. While males with the premutation of Fragile X were found to have difficulties in executive functions and working memory, little data have been collected on females. This study is among the first to address executive functions and phonological memory in females with the Fragile X premutation. Twenty-three female carriers aged 20–55 years and twelve non carrier females matched in age and levels of education (in years) participated in this study. Executive functions and phonological memory were assessed using the self-report questionnaire The Behavior Rating Inventory of Executive Function (BRIEF) and behavioral measures (nonword repetitions, forward and backward digit span). Females who were carriers of the premutation of the FMR1 gene reported less efficient executive functions in the BRIEF questionnaire compared to the control group. In addition, a relationship was found between the number of repetitions on the CGG sequence of nucleotides, nonword repetitions, and forward digit span. The findings suggest that the premutation of Fragile X in females affects their performance of executive functions and may have impact on everyday functioning.

Maternal FMR1 alleles expansion in newborns during transmission: a prospective cohort study

INTRODUCTION

The CGG repeats in the 5' untranslated region of the fragile X mental retardation 1 gene (FMR1) gene shows increased instability upon maternal transmission. Maternal FMR1 intermediate (45-54 repeats) and premutation (PM: 55-<200 repeats) alleles usually expand to full mutation (>200 repeats) alleles in offspring and consequently, cause fragile X syndrome (FXS) in them.

METHODS

In a prospective cohort study, Pakistani pregnant women in prenatal care were first screened for FMR1 expanded alleles. In the follow-up, pregnancy outcomes in women carrying FMR1 expanded alleles were recorded and their newborn offspring were also screened for FXS.

RESULTS

In a total of 1950 pregnant women, 89 (4.6%) were detected carriers for FMR1 expanded alleles; however, rates of detection of expanded alleles were found significantly high in women with a history of FXS. In addition, miscarriages and birth of affected newborns with FXS were significantly more common in women carrying large size PM alleles and had a history of FXS (P = 0.0494 and P = 0.0494, respectively).

CONCLUSIONS

The current study provides the first evidence of screening Pakistani pregnant women for FMR1 expanded alleles in prenatal care. Moreover, the miscarriage was also detected as a clinical predictor for FXS.

IMPACT

Offspring would have a higher risk of developing FXS due to maternal FMR1 alleles expansions during transmission. This is the first prospective cohort study in Pakistan for finding FMR1 allelic status of pregnant women and their newborn offspring in follow-up. The robust offspring risk for FXS estimated in this study may be valuable information for genetic counseling of women carriers for FMR1 expanded alleles. The family history and miscarriage were detected as effective indicators for FXS carrier screening in Pakistani women.

Characterization of a mGluR5 Knockout Rat Model with Hallmarks of Fragile X Syndrome

The number of reported cases of neurodevelopmental disorders has increased significantly in the last few decades, but the etiology of these diseases remains poorly understood. There is evidence of a fundamental link between genetic abnormalities and symptoms of autism spectrum disorders (ASDs), and the most common monogenetic inheritable form of ASDs is Fragile X Syndrome (FXS). Previous studies indicate that FXS is linked to glutamate signaling regulation by the G-protein-coupled metabotropic glutamate receptor 5 (mGluR5), which has been shown to have a regulatory role in neuroinflammation. We characterized the effect of knocking out mGluR5 in an organism known to have complex cognitive functions—the rat. The heterozygous phenotype is the most clinically relevant; therefore, we performed analysis in heterozygous pups. We showed developmental abnormalities in heterozygous mGluR5 knockout rats, as well as a significant increase in chemokine (C-X-C motif) ligand 1 (CXCL) expression, a hallmark indicator of early onset inflammation. We quantified an increase in microglial density in the knockout pups and quantified morphological phenotypes representative of greater reactivity in the male vs. female and postnatal day 28 heterozygous pups compared to postnatal day 14 heterozygous pups. In response to injury, reactive microglia release matrix metalloproteases, contribute to extracellular matrix (ECM) breakdown, and are responsible for eradicating cellular and molecular debris. In our study, the changes in microglial density and reactivity correlated with abnormalities in the mRNA expression levels of ECM proteins and with the density of perineuronal nets. We saw atypical neuropsychiatric behavior in open field and elevated plus tests in heterozygous pups compared to wild-type litter and age-matched controls. These results demonstrate the pathological potential of the mGluR5 knockout in rats and further support the presence of neuroinflammatory roots in ASDs.

Cognitive Dysfunction in Repeat Expansion Diseases: A Review

With the development of the sequencing technique, more than 40 repeat expansion diseases (REDs) have been identified during the past two decades. Moreover, the clinical features of these diseases show some commonality, and the nervous system, especially the cognitive function was affected in part by these diseases. However, the specific cognitive domains impaired in different diseases were inconsistent. Here, we survey literature on the cognitive consequences of the following disorders presenting cognitive dysfunction and summarizing the pathogenic genes, epidemiology, and different domains affected by these diseases. We found that the cognitive domains affected in neuronal intranuclear inclusion disease (NIID) were widespread including the executive function, memory, information processing speed, attention, visuospatial function, and language. Patients with C9ORF72-frontotemporal dementia (FTD) showed impairment in executive function, memory, language, and visuospatial function. While in Huntington's disease (HD), the executive function, memory, and information processing speed were affected, in the fragile X-associated tremor/ataxia syndrome (FXTAS), executive function, memory, information processing speed, and attention were impaired. Moreover, the spinocerebellar ataxias showed broad damage in almost all the cognitive domains except for the relatively intact language ability. Some other diseases with relatively rare clinical data also indicated cognitive dysfunction, such as myotonic dystrophy type 1 (DM1), progressive myoclonus epilepsy (PME), Friedreich ataxia (FRDA), Huntington disease like-2 (HDL2), and cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). We drew a cognitive function landscape of the related REDs that might provide an aspect for differential diagnosis through cognitive domains and effective non-specific interventions for these diseases.

Fragile X premutation carrier screening in Pakistani preconception women in primary care consultation

PURPOSE

Women of reproductive age who carry fragile X premutation (PM) alleles have 56 to 200 CGG repeats in the 5'-untranslated region of FMR1 gene are at increased risk for producing children with intellectual disabilities (ID) or autism spectrum disorders (ASD) due to expansion of PM alleles to full mutation alleles (> 200 repeats) during maternal transmission.

METHODS

In present study fragile X PM carrier screening was performed in total 808 women who were consulting primary health care centers for preconception care in Khyber Pakhtunkhwa region of Pakistan between April, 2018 and December, 2020. Polymerase chain reaction (PCR) was performed for detection of PM carrier women and the CGG repeats number was confirmed by Southern blotting and capillary electrophoresis.

RESULTS

The prevalence rate for PM carriers among preconception women was found to be 0.7% that was contributed by 0.5% women in risk group (RG1) with family history of ID and 0.2% in risk group 2 (RG2) with family history of ASD. PM carrier women had at least one affected child or sibling. In addition, the preconception women with FMR1 PM alleles were found to be at increased risk for primary ovary insufficiency (RG1: P = 0.0265, RG2: P = 0.0389), postpartum depression (RG1: P = 0.0240, RG2: P = 0.0501) and neuropsychiatric disorders (RG1: P = 0.0389, RG2: P = 0.0432).

CONCLUSIONS

Current study provides first evidence of fragile X PM carrier screening in Pakistani preconception women in primary care consultation. Findings of current study may help to improve preconception care and to reduce burden of fragile X associated disorders in our population.

Fragile X Syndrome Secondary to in Vitro Fertilization With a Family Egg Donor: A Case Report and Review of the Literature

Objective: To evidence the need for screening fragile X syndrome (FXS) in egg donors in assisted reproduction protocols.

Case report: This is the report of a boy with FXS who inherited the mutated allele from an ovule donated by the mother´s sister through an assisted reproduction protocol. Identifying premutation (PM) carriers of FXS amongst gamete donors isn’t part of the obligatory genetic analysis for donors and is only considered by most of the in vitro fertility societies and guidelines as part of the extension screening tests.

Conclusion: It is cost-effective to do pre-conceptional screening for the PM or full mutation (FM) of the FMR1 gene affected in FXS in every woman undergoing assisted reproductive methods, including gamete donors even without a positive family history of intellectual disabilities. This case supports the need of rethinking the guidelines on the necessary gamete donor screening tests in assisted reproduction protocols.

Fragile X Syndrome in a Female With Homozygous Full-Mutation Alleles of the FMR1 Gene

Fragile X syndrome (FXS) has been reported as the leading cause of mental retardation (MR) that predominantly involves males compared to females. An over-expansion of CGG repeats in the 5' untranslated region of the FMR1 gene plays the primary role in this disease. In this study, we encountered a homozygote female patient affected by FMR1 expansion mutation. Surprisingly, she had inherited her full-mutated alleles from two different ancestors. This condition is an extremely rare case of FXS. After accurate genetic counseling, family members were referred to the laboratory for genetic testing. Karyotype with two X chromosomes was the finding after the G-banding study of the proband. Molecular analysis indicated that she was a female with full-mutated or pre-mutated alleles on both of her X chromosomes. It is a rare phenomenon that we detected in this patient. We have concluded that a combination of allele instability during oogenesis and inheritance of two alleles are the leading cause of MR in the presented case.

Laboratory testing for fragile X, 2021 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG)

Molecular genetic testing of the FMR1 gene is commonly performed in clinical laboratories. Pathogenic variants in the FMR1 gene are associated with fragile X syndrome, fragile X-associated tremor ataxia syndrome (FXTAS), and fragile X-associated primary ovarian insufficiency (FXPOI). This document provides updated information regarding FMR1 pathogenic variants, including prevalence, genotype-phenotype correlations, and variant nomenclature. Methodological considerations are provided for Southern blot analysis and polymerase chain reaction (PCR) amplification of FMR1, including triplet repeat-primed and methylation-specific PCR.The American College of Medical Genetics and Genomics (ACMG) Laboratory Quality Assurance Committee has the mission of maintaining high technical standards for the performance and interpretation of genetic tests. In part, this is accomplished by the publication of the document ACMG Technical Standards for Clinical Genetics Laboratories, which is now maintained online ( http://www.acmg.net ). This subcommittee also reviews the outcome of national proficiency testing in the genetics area and may choose to focus on specific diseases or methodologies in response to those results. Accordingly, the subcommittee selected fragile X syndrome to be the first topic in a series of supplemental sections, recognizing that it is one of the most frequently ordered genetic tests and that it has many alternative methods with different strengths and weaknesses. This document is the fourth update to the original standards and guidelines for fragile X testing that were published in 2001, with revisions in 2005 and 2013, respectively.This versionClarifies the clinical features associated with different FMRI variants (Section 2.3)Discusses important reporting considerations (Section 3.3.1.3)Provides updates on technology (Section 4.1).

Response Inhibition Deficits in Women with the FMR1 Premutation are Associated with Age and Fall Risk

One in 113-178 females worldwide carry a premutation allele on the FMR1 gene. The FMR1 premutation is linked to neurocognitive and neuromotor impairments, although the phenotype is not fully understood, particularly with respect to age effects. This study sought to define oculomotor response inhibition skills in women with the FMR1 premutation and their association with age and fall risk. We employed an antisaccade eye-tracking paradigm to index oculomotor inhibition skills in 35 women with the FMR1 premutation and 28 control women. The FMR1 premutation group exhibited longer antisaccade latency and reduced accuracy relative to controls, indicating deficient response inhibition skills. Longer response latency was associated with older age in the FMR1 premutation and was also predictive of fall risk. Findings highlight the utility of the antisaccade paradigm for detecting early signs of age-related executive decline in the FMR1 premutation, which is related to fall risk. Findings support the need for clinical prevention efforts to decrease and delay the trajectory of age-related executive decline in women with the FMR1 premutation during midlife.

Systematic review of economic evaluation studies on preconception care interventions

Implementation of preconception care interventions have been encouraged for improving maternal and child health outcomes; therefore, evidence on their cost-effectiveness is needed. We conducted the systematic review to examine the efficiency of those interventions by collecting evidence from published economic evaluation studies. Out of 14 included studies, almost all (12/14) were in high-income countries. All studies were not cost-utility analysis with genetic disease screening and diabetes management were the common interventions for evaluating their efficiency during preconception period. Preconception care interventions are likely to be cost-effective, especially in low-income countries which incremental benefits had a greater return than developed nations.

Fragile X syndrome carrier screening accompanied by genetic consultation has clinical utility in populations beyond those recommended by guidelines

Background

Fragile X syndrome (FXS) is the most common inherited form of intellectual disability. Many providers offer preconception or prenatal FXS carrier screening. However, guidelines recommend screening only for those with a family history or undergoing fertility evaluation. Wider screening has been resisted because of concerns about patient understanding of FXS‐associated inheritance patterns and phenotypes. Additionally, the clinical utility has been questioned.

Methods

We addressed these concerns by analyzing reproductive decision‐making and pregnancy management informed by post‐test genetic consultation among 122 FMR1 premutation carriers identified by expanded carrier screening.

Results

Sixty‐three percent of those screened met guidelines screening criteria; the remaining 37% did not. Ninety‐eight percent had undergone post‐test genetic consultation. Of respondents screened preconceptionally, 74% reported planning or pursuing actions to reduce the risk of an affected pregnancy; the extent to which couples planned/pursued these actions was not significantly different between those meeting either screening criterion (76%) versus those meeting neither criterion (55%). Of respondents screened prenatally, 41% pursued prenatal diagnostic testing; the extent to which couples pursued prenatal diagnosis was not significantly different between those who met either screening criterion (37%) versus those who met neither criterion (31%).

Conclusion

These results support the expansion of FXS screening criteria in guidelines.

Fragile X syndrome carrier screening in pregnant women in Chinese Han population

Fragile X syndrome (FXS) is the most frequent genetic cause of intellectual disability (ID). It was previously believed that the FXS prevalence was low in Chinese population, and the cost-efficiency of FXS carrier screening was questioned. This retrospective observational study was conducted between September 2014 and May 2017 to determine the prevalence of FXS carriers in a large Chinese cohort of pregnant women. The FMR1 CGG repeat status was determined in 20,188 pregnant Taiwanese women and we identified 26 women with premutation (PM). The PM allele was transmitted to the fetus in 17 pregnancies (56.6%), and six of 17 expanded to full mutation (FM). One asymptomatic woman had a FM allele with 280 CGG repeats. Prenatal genetic diagnosis of her first fetus revealed a male carrying a FMR1 gene deletion of 5′ UTR and exon 1. Her second fetus was a female carrying a FM allele as well. This is so far the largest study of the FXS carrier screening in Chinese women. The prevalence of premutation allele for FXS in normal asymptomatic Taiwanese women was found to be as high as 0.13% (1 in 777) in this study. The empirical evidence suggests that reproductive FXS carrier screening in Taiwan might be cost-effective.

Analysis of economic burden and its associated factors of twenty-three rare diseases in Shanghai

Background

It is estimated that at present there are over 10 million rare disease patients in China. Recently an increased focus from policy perspective has been placed on rare diseases management. Improved disease definitions and the releases of local and national rare disease lists are some of the steps taken already. Despite these developments, few Chinese rare disease-related epidemiology and economic studies exist, thus hindering assessment of the true burden of rare diseases. For a rare disease with an effective treatment, this is a particularly important aspect due to the often-high cost associated.

Objective

The goal of this study is to address the data scarcity on the subject of rare diseases economic impact in China. We aim to address an existing knowledge gap and to provide a timely analysis of the economic burden of 23 rare diseases in Shanghai, China.

Methods

We utilized the data from the Health Information Exchange system of Shanghai and employed statistical modeling to analyze the economic burden of rare diseases with an effective treatment in Shanghai.

Results

First, we described the actual direct medical expenditure and analyzed its associated factors. Second, we found age, disease type, number of complications, and payment type were significantly associated with rare disease medical direct costs. Third, a generalized linear model was employed to estimate the annual direct cost. The mean direct medical cost was estimated as ¥9588 (US$1521) for inpatients and ¥1060 (US$168) for outpatients, and was over ¥15 million (~US$2.4 million) per year overall.

Conclusion

Our study is one of the first quantifying the economic burden of an extensive set of rare diseases in Shanghai and China. Our results can serve to inform healthcare-focused policy making, contribute to the increase of public awareness, and incentivize development of rare-disease strategies and treatments specific to the Chinese context.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1168-4) contains supplementary material, which is available to authorized users.

The role of AGG interruptions in the FMR1 gene stability: A survey in ethnic groups with low and high rate of consanguinity

Background

The prevalence and the role of AGG interruptions within the FMR1 gene in the normal population is unknown. In this study, we investigated the frequent of AGG loss, in one or two alleles within the normal population. The role of AGG in the FMR1 stability has been assessed by correlating AGG loss to the prevalence of premutation/full mutation in two ethnic groups differing in their consanguinity rate: high versus low consanguinity rate (HCR vs. LCR).

Methods

The CGG repeat allele size and AGG presence were measured in 6,865 and 6,204 females belonging to the LCR (5%) and HCR (>45%) groups, respectively, by Tripled‐Primed‐PCR technique.

Results

A lower prevalence of the premutation was observed in the HCR (1:158) as compared to the LCR group (1:128). No full mutation was found in the HCR females while in the LCR group the prevalence found was 1:1,149. Homozygosity rate was higher in the HCR population compared to the LCR group.The overall AGG loss was higher in the HCR population than in the LCR and increased with increased CGG repeat number in both ethnic groups.

Conclusions

Although we observed a significantly higher rate of homozygosity and AGG loss in the HCR group, this did not affect the prevalence of the premutation and full mutation in this population. Their prevalence was significantly lower than in the LCR population. Finally, we discuss whether the loss of AGG could be also a polymorphic event but not only a stabilizing factor.

The prevalence of CGG repeat expansion mutation in FMR1 gene in the northern Chinese women of reproductive age

BACKGROUND

The prevalence of CGG repeat expansion mutation in FMR1 gene varies among different populations. In this study, we investigated the prevalence of this mutation in women of reproductive age from northern China.

METHODS

A total of 11,891 pre-conceptional or pregnant women, including 5037 pregnant women and 7357 women with the history of spontaneous abortion or induced abortion due to delayed growth of the embryos, were recruited. The number of CGG repeats in FMR1 was measured by the TRP-PCR method. We also offered genetic counseling and prenatal diagnosis to the women carrying pre-mutation or full mutation alleles.

RESULTS

The prevalence of pre-mutation in reproductive women in northern China was 1/410, higher than that in southern China and Korea but lower than that in western countries. We also found that the prevalence of pre-mutation was relatively high (1/320) in women with abortion history.

CONCLUSION

Screening for CGG repeat expansion mutation in FMR1 should be recommended to the women with the history of spontaneous abortion or induced abortion due to delayed growth of the embryos.

Genetics and genomic medicine in Tunisia

Genetics and genomic medicine in Tunisia.

Are expanded alleles of the FMR1 gene related to unexplained recurrent miscarriages?

BACKGROUND

In women with recurrent miscarriages, up to 50 % of those cases remain unexplained. In this study, we evaluated the impact of Cytosine/Guanine/Guanine (CGG)  trinucleotide expansions of the fragile-X mental retardation 1 (FMR1) gene in women with unexplained recurrent miscarriages.

METHODS

This is a prospective case-control pilot study involving 49 women with unexplained recurrent miscarriages and 49 age-matched controls with documented fertility. The case group consisted of women with a history of two or more consecutive miscarriages, in whom no known factor could be identified. The maximum age of recruitment was 40 years. We obtained blood samples that were checked, using polymerase chain reaction with electrophoresis, for the presence of expanded alleles of the FMR1 gene. We further evaluated using sequencing analysis, those women marked as positive. We set the limit at more than 40 repeats.

RESULTS

The repeat sizes of CGG expansion in the FMR1 gene differ significantly in the two population groups (p =0.027). We found four women in the miscarriage group and one in the control group positive for carrying premutation alleles (Odds ratio: 4.267, confidence interval: 0.459-39.629). All the positive cases involved intermediate zone carriers. We found no association between the number of abortions each woman had, and her respective CGG repeat number (p =0.255).

CONCLUSIONS

Many couples are desperately looking for the cause of their recurrent miscarriage suffering. The CGG expanded allele of the FMR1 gene is possibly to be blamed in some of these cases. More studies are needed to support the results of this prototype study. HIPPOKRATIA 2018, 22(3): 132-136.

Prolonged Time Lag to Final Diagnosis of Fragile X Syndrome

OBJECTIVE

To evaluate the diagnostic process in children ultimately diagnosed with fragile X syndrome (FXS), with an emphasis on the time lag between initial presentation and on diagnosis in female vs male children.

STUDY DESIGN

Interviews were conducted with 89 families of children with a final diagnosis of FXS and assessment of time intervals between initial presentation and confirmed molecular diagnosis.

RESULTS

Screening of 117 patients (25 female patients) from the 89 families revealed that less than 20% of patients obtained a diagnosis within the first year of seeking medical attention. Mean age at the time of initial presentation was 12.3 months in male patients and 23 months in female patients, while definitive diagnosis of FXS was made at a mean of 4 and 9 years, respectively. Presenting symptoms of developmental delays were recognized by 72% of parents, and 84% had another child with FXS before the index case diagnosis. Average age of diagnosis for children with FXS born since 2007 was significantly lower at 31.9 months, compared with 69.5 months for children born before 2007.

CONCLUSIONS

Although FXS is a significant and prevalent cause of disability in children, it is underdiagnosed and diagnosed late, especially in female patients. In every male and female patient presenting with developmental delay or autism, FXS should be considered. Dysmorphic physical features may not be present in infancy, and the absence of those features cannot exclude a diagnosis of FXS.

Expanded alleles of the FMR1 gene are related to unexplained recurrent miscarriages

Up to 50% of recurrent miscarriage cases in women occur without an underlying etiology. In the current prospective case-control study, we determined the impact of CGG trinucleotide expansions of the fragile-X mental retardation 1 (FMR1) gene in 49 women with unexplained recurrent miscarriages. Case group consisted of women with two or more unexplained consecutive miscarriages. Blood samples were obtained and checked for the presence of expanded alleles of the FMR1 gene using PCR. Patients harboring the expanded allele, with a threshold set to 40 repeats, were further evaluated by sequencing. The number of abortions each woman had, was not associated with her respective CGG repeat number (P=0.255). The repeat sizes of CGG expansion in the FMR1 gene were significantly different in the two population groups (P=0.027). All the positive cases involved intermediate zone carriers. Hence, the CGG expanded allele of the FMR1 gene might be associated with unexplained multiple miscarriages; whether such an association is coincidental or causal can be confirmed by future studies using a larger patient cohort.

Molecular Characterization of FMR1 Gene by TP-PCR in Women of Reproductive Age and Women with Premature Ovarian Insufficiency

BACKGROUND

Fragile X syndrome is caused by CGG repeat expansion mutation in the FMR1 gene. Normal alleles have 5-44 CGG repeats with AGG interruptions. The expanded gray zone (GZ) (45-54 repeats) and premutation (PM) (55-200 repeats) alleles are often uninterrupted and are unstably inherited in subsequent generations. The prevalence of PM and GZ carriers is high in the female population, at 1/66 and 1/113, respectively, and PM is associated with fertility problems in 20% of cases.

OBJECTIVE

Our objective was to molecularly characterize CGG repeats and AGG interruption sequences in the FMR1 gene in women of reproductive age and in women with premature ovarian insufficiency (POI).

MATERIALS AND METHODS

We conducted molecular analysis of the FMR1 gene from 300 women of reproductive age and 140 women with POI using triplet primed-polymerase chain reaction. This enabled us to identify carriers and to document CGG repeat size and the AGG interruption pattern.

RESULTS

In women of reproductive age, 1.7% were GZ carriers and 0.3% were PM carriers; in women with POI, 3.6% were GZ carriers and 2.14% were PM carriers. The frequency of GZ and PM carriers did not significantly differ between the cohorts (Fisher's exact test: p < 2.23 for GZ vs. control and p < 0.101 for PM vs. control). Carriers received genetic counselling; family screening identified an additional seven carriers.

CONCLUSION

We documented preliminary data on the prevalence of GZ and PM carriers among the studied cohorts. The identification of PM carriers among women with POI serves a dual purpose of recognizing a cause for ovarian dysfunction and enabling genetic counselling, which will help carriers when making reproductive decisions.

FMR1 CGG repeat expansion mutation detection and linked haplotype analysis for reliable and accurate preimplantation genetic diagnosis of fragile X syndrome

Fragile X mental retardation 1 (FMR1) full-mutation expansion causes fragile X syndrome. Trans-generational fragile X syndrome transmission can be avoided by preimplantation genetic diagnosis (PGD). We describe a robust PGD strategy that can be applied to virtually any couple at risk of transmitting fragile X syndrome. This novel strategy utilises whole-genome amplification, followed by triplet-primed polymerase chain reaction (TP-PCR) for robust detection of expanded FMR1 alleles, in parallel with linked multi-marker haplotype analysis of 13 highly polymorphic microsatellite markers located within 1 Mb of the FMR1 CGG repeat, and the AMELX/Y dimorphism for gender identification. The assay was optimised and validated on single lymphoblasts isolated from fragile X reference cell lines, and applied to a simulated PGD case and a clinical in vitro fertilisation (IVF)-PGD case. In the simulated PGD case, definitive diagnosis of the expected results was achieved for all ‘embryos’. In the clinical IVF-PGD case, delivery of a healthy baby girl was achieved after transfer of an expansion-negative blastocyst. FMR1 TP-PCR reliably detects presence of expansion mutations and obviates reliance on informative normal alleles for determining expansion status in female embryos. Together with multi-marker haplotyping and gender determination, misdiagnosis and diagnostic ambiguity due to allele dropout is minimised, and couple-specific assay customisation can be avoided.

Fragile X Newborn Screening: Lessons Learned From a Multisite Screening Study

BACKGROUND

Delays in the diagnosis of children with fragile X syndrome (FXS) suggest the possibility of newborn screening as a way to identify children earlier. However, FXS does not have a proven treatment that must be provided early, and ethical concerns have been raised about the detection of infants who are carriers. This article summarizes major findings from a multisite, prospective, longitudinal pilot screening study.

METHODS

Investigators in North Carolina, California, and Illinois collaborated on a study in which voluntary screening for FXS was offered to parents in 3 birthing hospitals. FXS newborn screening was offered to >28 000 families to assess public acceptance and determine whether identification of babies resulted in any measurable harms or adverse events. Secondary goals were to determine the prevalence of FMR1 carrier gene expansions, study the consent process, and describe early development and behavior of identified children.

RESULTS

A number of publications have resulted from the project. This article summarizes 10 "lessons learned" about the consent process, reasons for accepting and declining screening, development and evaluation of a decision aid, prevalence of carriers, father participation in consent, family follow-up, and maternal reactions to screening.

CONCLUSIONS

The project documented public acceptance of screening as well as the challenges inherent in obtaining consent in the hospital shortly after birth. Collectively, the study provides answers to a number of questions that now set the stage for a next generation of research to determine the benefits of earlier identification for children and families.

Reduced vagal tone in women with the FMR1 premutation is associated with FMR1 mRNA but not depression or anxiety

Background

Autonomic dysfunction is implicated in a range of psychological conditions, including depression and anxiety. The fragile X mental retardation-1 (FMR1) premutation is a common genetic mutation that affects ~1:150 women and is associated with psychological vulnerability. This study examined cardiac indicators of autonomic function among women with the FMR1 premutation and control women as potential biomarkers for psychological risk that may be linked to FMR1.

Methods

Baseline inter-beat interval and respiratory sinus arrhythmia (a measure of parasympathetic vagal tone) were measured in 35 women with the FMR1 premutation and 28 controls. The women completed anxiety and depression questionnaires. FMR1 genetic indices (i.e., CGG repeat, quantitative FMRP, FMR1 mRNA, activation ratio) were obtained for the premutation group.

Results

Respiratory sinus arrhythmia was reduced in the FMR1 premutation group relative to controls. While depression symptoms were associated with reduced respiratory sinus arrhythmia among control women, these variables were unrelated in the FMR1 premutation. Elevated FMR1 mRNA was associated with higher respiratory sinus arrhythmia.

Conclusions

Women with the FMR1 premutation demonstrated autonomic dysregulation characterized by reduced vagal tone. Unlike patterns observed in the general population and in study controls, vagal activity and depression symptoms were decoupled in women with the FMR1 premutation, suggesting independence between autonomic regulation and psychopathological symptoms that is atypical and potentially specific to the FMR1 premutation. The association between vagal tone and mRNA suggests that molecular variation associated with FMR1 plays a role in autonomic regulation.

Fragile X syndrome screening in pregnant women and women planning pregnancy shows a remarkably high FMR1 premutation prevalence in the Balearic Islands

There are no reported studies to determine incidence of Fragile X Syndrome (FXS) in women within the Spanish population. For this reason, together with the high incidence of FXS in the general population, the exclusively maternal expansion, the familial and social impact of the syndrome, and the ease of use and level of detection of current PCR-based techniques, we have conducted a population-based screening pilot program of which we present here the molecular results. We typed prospectively 3,413 pregnant and 318 non-pregnant women and found a prevalence of premutation (PM) carriers of 1 in 106, which is the highest described to date in any population. We also found 230 different alleles of which the most frequent are 10A9A9 (38.4%), 9A9A9 (15.1%), and 10A9 (10.5%). Furthermore, alleles with 0 AGG interruptions or with a pure (uninterrupted) CGG repeat run larger than 34 (presumably more unstable), were more frequent among PM alleles compared to normal alleles. Theà unexpected high frequency of expanded PM alleles in females in the general population makes a very compelling argument for the need for prenatal or preconceptional FXS screening in our community. Furthermore, we find FMR1 triplet primed PCR (TP-PCR) confidently and precisely determines sizes for both alleles of the CGG repeat in women and offers AGG information which greatly improves CGG expansion risk estimations for genetic counselling. Thus, TP-PCR is an informative, efficient and robust method for FXS screening in the female population. © 2016 Wiley Periodicals, Inc.

Development of Genetic Testing for Fragile X Syndrome and Associated Disorders, and Estimates of the Prevalence of FMR1 Expansion Mutations

The identification of a trinucleotide (CGG) expansion as the chief mechanism of mutation in Fragile X syndrome in 1991 heralded a new chapter in molecular diagnostic genetics and generated a new perspective on mutational mechanisms in human genetic disease, which rapidly became a central paradigm (“dynamic mutation”) as more and more of the common hereditary neurodevelopmental disorders were ascribed to this novel class of mutation. The progressive expansion of a CGG repeat in the FMR1 gene from “premutation” to “full mutation” provided an explanation for the “Sherman paradox,” just as similar expansion mechanisms in other genes explained the phenomenon of “anticipation” in their pathogenesis. Later, FMR1 premutations were unexpectedly found associated with two other distinct phenotypes: primary ovarian insufficiency and tremor-ataxia syndrome. This review will provide a historical perspective on procedures for testing and reporting of Fragile X syndrome and associated disorders, and the population genetics of FMR1 expansions, including estimates of prevalence and the influence of AGG interspersions on the rate and probability of expansion.

Prognostic dilemmas and genetic counseling for prenatally detected fragile X gene expansions

With widespread adoption of fragile X carrier screening in pregnant women, the number of expectant couples receiving news of an unanticipated Fragile X Mental Retardation 1 (FMR1) gene expansion has increased. The most common abnormal result from maternal FMR1 testing involves an intermediate allele, also known as a gray zone result, which requires genetic counseling but poses minimal risk for an adverse developmental outcome. By contrast, the finding of a maternal FMR1 premutation or full mutation during pregnancy has important implications for the woman herself, her unborn child, and her extended family. These multiple levels of impact, in addition to the complex inheritance pattern and variable expressivity of fragile X-associated disorders, cause significant stress for newly identified expectant couples and pose unique challenges for genetic counselors in the prenatal setting. © 2016 John Wiley & Sons, Ltd.

Molecular Correlates and Recent Advancements in the Diagnosis and Screening of FMR1-Related Disorders

Fragile X syndrome (FXS) is the most common monogenic cause of intellectual disability and autism. Molecular diagnostic testing of FXS and related disorders (fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor/ataxia syndrome (FXTAS)) relies on a combination of polymerase chain reaction (PCR) and Southern blot (SB) for the fragile X mental retardation 1 (FMR1) CGG-repeat expansion and methylation analyses. Recent advancements in PCR-based technologies have enabled the characterization of the complete spectrum of CGG-repeat mutation, with or without methylation assessment, and, as a result, have reduced our reliance on the labor- and time-intensive SB, which is the gold standard FXS diagnostic test. The newer and more robust triplet-primed PCR or TP-PCR assays allow the mapping of AGG interruptions and enable the predictive analysis of the risks of unstable CGG expansion during mother-to-child transmission. In this review, we have summarized the correlation between several molecular elements, including CGG-repeat size, methylation, mosaicism and skewed X-chromosome inactivation, and the extent of clinical involvement in patients with FMR1-related disorders, and reviewed key developments in PCR-based methodologies for the molecular diagnosis of FXS, FXTAS and FXPOI, and large-scale (CGG)_n expansion screening in newborns, women of reproductive age and high-risk populations.

A Pilot Study of Fragile X Syndrome Screening in Pregnant Women and Women Planning Pregnancy: Implementation, Acceptance, Awareness, and Geographic Factors

We report herein results of a study performed in the Balearic Islands which had the following goals: 1) Determine the proportion of pregnant or non-pregnant women planning pregnancy, who would choose to undergo a screening test for Fragile X Syndrome (FXS), if it is accompanied by the appropriate information; 2) Assess satisfaction and any increase in stress among women who participate in screening; 3) Collect epidemiological information about the incidence of the disease in our population; and 4) Collect demographic and health history data and assess participants' awareness of the disease. Screening was performed on 3,731 pregnant and non-pregnant women of childbearing age and the results indicate: a very high voluntary rate of participation; a high level of self-reported satisfaction and low levels of stress because of the test; a very high incidence of premutation (1/106) in our population; and a low level of awareness about the existence of FXS (25 %). Additional findings indicate no significant correlation between self-reported health history and premutation detection, and the high premutation incidence does not seem to be specific to the indigenous Balearic population. Based on these results, we discuss the pros and cons of an implementation of preconception and pregnant women screening for FXS within a public health screening program.

The impact of FMR1 gene mutations on human reproduction and development: a systematic review

PURPOSE

This is a comprehensive review of the literature in this field attempting to put the FMR1 gene and its evaluation into context, both in general and for the reproductive health audience.

METHODS

Online database search of publications with systematic review of all papers relevant to ovarian reserve and assisted reproduction was done.

RESULTS

Relevant papers were identified and assessed, and an attempt was made to understand, rationalize and explain the divergent views in this field of study. Seminal and original illustrations were employed.

CONCLUSIONS

FMR1 is a highly conserved gene whose interpretation and effect on outcomes remains controversial in the reproductive health setting. Recent re-evaluations of the commonly accepted normal range have yielded interesting tools for possibly explaining unexpected outcomes in assisted reproduction. Fragile X investigations should perhaps become more routinely assessed in the reproductive health setting, particularly following a failed treatment cycle where oocyte quality is thought to be a contributing factor, or in the presence of a surprise finding of diminished ovarian reserve in a young patient.

Programming social behavior by the maternal fragile X protein

The developing fetus and neonate are highly sensitive to maternal environment. Besides the well-documented effects of maternal stress, nutrition and infections, maternal mutations, by altering the fetal, perinatal and/or early postnatal environment, can impact the behavior of genetically normal offspring. Mutation/premutation in the X-linked FMR1 (encoding the translational regulator FMRP) in females, although primarily responsible for causing fragile X syndrome (FXS) in their children, may also elicit such maternal effects. We showed that a deficit in maternal FMRP in mice results in hyperactivity in the genetically normal offspring. To test if maternal FMRP has a broader intergenerational effect, we measured social behavior, a core dimension of neurodevelopmental disorders, in offspring of FMRP-deficient dams. We found that male offspring of Fmr1(+/-) mothers, independent of their own Fmr1 genotype, exhibit increased approach and reduced avoidance toward conspecific strangers, reminiscent of 'indiscriminate friendliness' or the lack of stranger anxiety, diagnosed in neglected children and in patients with Asperger's and Williams syndrome. Furthermore, social interaction failed to activate mesolimbic/amygdala regions, encoding social aversion, in these mice, providing a neurobiological basis for the behavioral abnormality. This work identifies a novel role for FMRP that extends its function beyond the well-established genetic function into intergenerational non-genetic inheritance/programming of social behavior and the corresponding neuronal circuit. As FXS premutation and some psychiatric conditions that can be associated with reduced FMRP expression are more prevalent in mothers than full FMR1 mutation, our findings potentially broaden the significance of FMRP-dependent programming of social behavior beyond the FXS population.

Multiple Drug Treatments That Increase cAMP Signaling Restore Long-Term Memory and Aberrant Signaling in Fragile X Syndrome Models

Fragile X is the most common monogenic disorder associated with intellectual disability (ID) and autism spectrum disorders (ASD). Additionally, many patients are afflicted with executive dysfunction, ADHD, seizure disorder and sleep disturbances. Fragile X is caused by loss of FMRP expression, which is encoded by the FMR1 gene. Both the fly and mouse models of fragile X are also based on having no functional protein expression of their respective FMR1 homologs. The fly model displays well defined cognitive impairments and structural brain defects and the mouse model, although having subtle behavioral defects, has robust electrophysiological phenotypes and provides a tool to do extensive biochemical analysis of select brain regions. Decreased cAMP signaling has been observed in samples from the fly and mouse models of fragile X as well as in samples derived from human patients. Indeed, we have previously demonstrated that strategies that increase cAMP signaling can rescue short term memory in the fly model and restore DHPG induced mGluR mediated long term depression (LTD) in the hippocampus to proper levels in the mouse model (McBride et al., 2005; Choi et al., 2011, 2015). Here, we demonstrate that the same three strategies used previously with the potential to be used clinically, lithium treatment, PDE-4 inhibitor treatment or mGluR antagonist treatment can rescue long term memory in the fly model and alter the cAMP signaling pathway in the hippocampus of the mouse model.

Distribution of fragile X mental retardation 1 CGG repeat and flanking haplotypes in a large Chinese population

Fragile X syndrome is mainly caused by a CGG repeat expansion within the 5' UTR of the fragile X mental retardation 1 (FMR1) gene. Previous analyses of the FMR1 CGG repeat patterns and flanking haplotypes in Caucasians and African Americans have identified several factors that may influence repeat instability. However, the CGG repeat patterns and distribution for FRAXAC2 have not yet been investigated in mainland Chinese. We surveyed the CGG repeat lengths in 1113 Han Chinese (534 males and 579 females), and the CGG repeat patterns of 534 males were determined by sequence analysis. We also explored the flanking haplotypes (DXS548-FRAXAC1-FRAXAC2) in 566 unaffected and 28 unrelated fragile X Chinese males. The most frequent alleles for DXS548 and FRAXAC1 were identical between our Chinese population and other Asian populations. We identified several low-abundance alleles for DXS548 and FRAXAC1 not found in previous studies in mainland Chinese and Taiwanese cohorts. The most frequent allele was (CGG)29 followed by (CGG)30, and the most frequent patterns were 9 + 9 + 9, 10 + 9 + 9, and 9 + 9 + 6 + 9, similar to those in Singaporeans. We identified only one premutation female carrier with 89 CGG repeats in the 1113 Han Chinese. A few associations between the CGG repeat patterns and flanking haplotypes were determined in this study. In general, the Chinese population had a smaller number of alleles and lower expected heterozygosity for all three STR markers and FRAXA locus when compared with Caucasians and African Americans. We identified a novel haplotype 7-3-5 + that is significantly associated with the full mutation.

Intermediate CGG repeat length at the FMR1 locus is not associated with hormonal indicators of ovarian age

OBJECTIVE

Premutation and intermediate CGG repeat length at the fragile X mental retardation 1 (FMR1) locus have been associated with premature ovarian failure. We tested whether intermediate length is associated with indicators of ovarian age in a sample of fertile women. Our primary measures of ovarian age were antimüllerian hormone (AMH) and follicle-stimulating hormone (FSH) levels.

METHODS

The cross-sectional sample comprised 258 women with karyotyped spontaneous abortions (140 trisomic spontaneous abortions and 118 chromosomally normal spontaneous abortions or spontaneous abortions with anomalies other than trisomy) and 325 women with recent live births (LBs). We analyzed data from the total sample and data from LBs only. We defined CGG repeat length by the length (both continuous and categorical) on the longer allele.

RESULTS

CGG repeat length was not significantly associated with either hormone measure. A repeat length of 35 to 54 CGG, versus the modal category of 30 CGG, was associated with an approximately 7% increase in median AMH level and a 3% increase in median FSH level. Results were unaltered when analyses were limited to LBs. Analyses of hormone levels using cutpoints to define older ovarian age showed no associations with repeat length. Among 10 women with repeat lengths of 35 to 54 CGG analyzed for AGG sequences, the uninterrupted CGG length was not significantly longer among women with hormonal indicators of "old" versus "young" ovarian age.

CONCLUSIONS

Our data do not support an association between intermediate CGG repeat length and levels of AMH or FSH among fertile women.

Psychological status in female carriers of premutation FMR1 allele showing a complex relationship with the size of CGG expansion

We utilized a sample of 299 adult females aged between 19 and 86 years, carrying fragile X mental retardation (FMR1) alleles with small CCG expansions ranging from 50 to 141 repeats to analyse the relationships between psychological symptoms as assessed by the Symptom Checklist-90-Revised (SCL-90-R) and the size of the CGG repeat in the FMR1 gene. There were highly significant (negative) correlations between the size of the CGG repeat and a great majority of SCL-90-R subscale scores and all the global indices, suggesting that carriers of premutations in the mid-size CGG repeat range may be at greatest risk for the development of psychiatric disorder.

Socio-economic burden of rare diseases: A systematic review of cost of illness evidence

Cost-of-illness studies, the systematic quantification of the economic burden of diseases on the individual and on society, help illustrate direct budgetary consequences of diseases in the health system and indirect costs associated with patient or carer productivity losses. In the context of the BURQOL-RD project ("Social Economic Burden and Health-Related Quality of Life in patients with Rare Diseases in Europe") we studied the evidence on direct and indirect costs for 10 rare diseases (Cystic Fibrosis [CF], Duchenne Muscular Dystrophy [DMD], Fragile X Syndrome [FXS], Haemophilia, Juvenile Idiopathic Arthritis [JIA], Mucopolysaccharidosis [MPS], Scleroderma [SCL], Prader-Willi Syndrome [PWS], Histiocytosis [HIS] and Epidermolysis Bullosa [EB]). A systematic literature review of cost of illness studies was conducted using a keyword strategy in combination with the names of the 10 selected rare diseases. Available disease prevalence in Europe was found to range between 1 and 2 per 100,000 population (PWS, a sub-type of Histiocytosis, and EB) up to 42 per 100,000 population (Scleroderma). Overall, cost evidence on rare diseases appears to be very scarce (a total of 77 studies were identified across all diseases), with CF (n=29) and Haemophilia (n=22) being relatively well studied, compared to the other conditions, where very limited cost of illness information was available. In terms of data availability, total lifetime cost figures were found only across four diseases, and total annual costs (including indirect costs) across five diseases. Overall, data availability was found to correlate with the existence of a pharmaceutical treatment and indirect costs tended to account for a significant proportion of total costs. Although methodological variations prevent any detailed comparison between conditions and based on the evidence available, most of the rare diseases examined are associated with significant economic burden, both direct and indirect.

Current research, diagnosis, and treatment of fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is caused by a premutation CGG-repeat expansion in the 5'UTR of the fragile X mental retardation 1 (FMR1) gene. The classical clinical manifestations include tremor, cerebellar ataxia, cognitive decline and psychiatric disorders. Other less frequent features are peripheral neuropathy and autonomic dysfunction. Cognitive decline, a form of frontal subcortical dementia, memory loss and executive function deficits are also characteristics of this disorder. In this review, we present an expansion of recommendations for genetic testing for adults with suspected premutation disorders and provide an update of the clinical, radiological and molecular research of FXTAS, as well as the current research in the treatment for this intractable complex neurodegenerative genetic disorder.

FMR1 CGG allele length in Israeli BRCA1/BRCA2 mutation carriers and the general population display distinct distribution patterns

Premature ovarian failure and diminished ovarian reserve have been noted both in female BRCA1/BRCA2 mutation carriers and in carriers of the Fragile X syndrome FMR1 gene CGG repeat size premutation. Based on the observation that BRCA mutation carriers do not harbour long CGG repeats in the FMR1 gene, it was hypothesized that BRCA-associated premature ovarian failure is mediated via FMR1. To test this notion, we evaluated the distribution of constitutional FMR1 genotypes in 188 BRCA1/BRCA2 mutation-positive Jewish Ashkenazi women and 15 708 female, mostly Ashkenazi controls in Israel. BRCA1/BRCA2 mutation carriers displayed a unique distribution of FMR1 genotypes compared with controls (p = 0·018) with a prominence of the shorter CGG alleles (<26 repeats). There was no allele size distribution differences within BRCA carriers when comparing cancer free (n = 95) and breast cancer affected women (n = 93) (p = 0·43). In conclusion, BRCA mutation carriers exhibit a distinct CGG FMR1 repeat size pattern compared with the general population, but it is unlikely to account for the reported diminished ovarian reserve or act as a modifier breast cancer gene in BRCA mutation carriers.

Ethnic effect on FMR1 carrier rate and AGG repeat interruptions among Ashkenazi women

PURPOSE

Fragile X syndrome, a common cause of intellectual disability, is usually caused by CGG trinucleotide expansion in the FMR1 gene. CGG repeat size correlates with expansion risk. Premutation alleles (55-200 repeats) may expand to full mutations in female meiosis. Interspersed AGG repeats decrease allele instability and expansion risk. The carrier rate and stability of FMR1 alleles were evaluated in large cohorts of Ashkenazi and non-Ashkenazi women.

METHODS

A total of 4,344 Ashkenazi and 4,985 non-Ashkenazi cases were analyzed using Southern blotting and polymerase chain reaction between 2004 and 2011. In addition, AGG interruptions were evaluated in 326 Ashkenazi and 298 non-Ashkenazi women who were recruited during 2011.

RESULTS

Both groups had major peaks of 30 and 29 repeats. Ashkenazi women had a higher frequency of 30 repeats and a lower frequency of other peaks (P < 0.0001). A higher rate of premutations in the 55-59 repeats range (1:114 vs. 1:277) was detected among the Ashkenazi women. Loss of AGG interruptions (<2) was significantly less common among Ashkenazi women (9 vs. 19.5% for non-Ashkenazi women, P = 0.0002).

CONCLUSION

Ashkenazi women have a high fragile X syndrome carrier rate and mostly lower-range premutations, and carry a low risk for expansion to a full mutation. Normal-sized alleles in Ashkenazi women have higher average number of AGG interruptions that may increase stability. These factors may decrease the risk for fragile X syndrome offspring among Ashkenazi women.

Why do fragile X carrier frequencies differ between Asian and non-Asian populations?

Asian and non-Asian populations have been reported to differ substantially in the distribution of fragile X alleles into the normal (< 55 CGG repeats), premutation (55-199 CGG repeats), and full-mutation (> 199 CGG repeats) size classes. Our statistical analyses of data from published general-population studies confirm that Asian populations have markedly lower frequencies of premutation alleles, reminiscent of earlier findings for expanded alleles at the Huntington's Disease locus. To examine historical and contemporary factors that may have shaped and now sustain allele-frequency differences at the fragile X locus, we develop a population-genetic/epigenetic model, and apply it to these published data. We find that founder-haplotype effects likely contribute to observed frequency differences via substantially lower mutation rates in Asian populations. By contrast, any premutation frequency differences present in founder populations would have disappeared in the several millennia since initial establishment of these groups. Differences in the reproductive fitness of female premutation carriers arising from fragile X primary ovarian insufficiency (FXPOI) and from differences in mean maternal age may also contribute to global variation in carrier frequencies.

Psychological status in female carriers of premutation FMR1 allele showing a complex relationship with the size of CGG expansion

We utilized a sample of 299 adult females aged between 19 and 86 years, carrying fragile X mental retardation (FMR1) alleles with small CCG expansions ranging from 50 to 141 repeats to analyse the relationships between psychological symptoms as assessed by the Symptom Checklist-90-Revised (SCL-90-R) and the size of the CGG repeat in the FMR1 gene. There were highly significant (negative) correlations between the size of the CGG repeat and a great majority of SCL-90-R subscale scores and all the global indices, suggesting that carriers of premutations in the mid-size CGG repeat range may be at greatest risk for the development of psychiatric disorder.

Investigation of memory, executive functions, and anatomic correlates in asymptomatic FMR1 premutation carriers

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset movement disorder associated with FMR1 premutation alleles. Asymptomatic premutation (aPM) carriers have preserved cognitive functions, but they present subtle executive deficits. Current efforts are focusing on the identification of specific cognitive markers that can detect aPM carriers at higher risk of developing FXTAS. This study aims at evaluating verbal memory and executive functions as early markers of disease progression while exploring associated brain structure changes using diffusion tensor imaging. We assessed 30 aPM men and 38 intrafamilial controls. The groups perform similarly in the executive domain except for decreased performance in motor planning in aPM carriers. In the memory domain, aPM carriers present a significant decrease in verbal encoding and retrieval. Retrieval is associated with microstructural changes of the white matter (WM) of the left hippocampal fimbria. Encoding is associated with changes in the WM under the right dorsolateral prefrontal cortex, a region implicated in relational memory encoding. These associations were found in the aPM group only and did not show age-related decline. This may be interpreted as a neurodevelopmental effect of the premutation, and longitudinal studies are required to better understand these mechanisms.